The effectiveness of EPS geofoam compressible inclusions in reducing both the seismic earth pressure and displacement increment (i.e., horizontal translation and rotation) of yielding, gravity type, earth retaining walls, was investigated by parametric numerical analyses. The 2-D finite element code PLAXIS was used for analyzing the seismic response of two gravity-type retaining walls (with heights equal to 4 m and 7.5 m) under harmonic excitation at the wall base of varying amplitude (0.1 g to 0.7 g) and frequency (0.3 Hz to 20 Hz). The isolation efficiency of the inclusions (defined as the ratio of displacement or pressure reduction, due to inclusion, to the corresponding values for a non-isolated wall) was studied as a function of the normalized - with respect to wall height - thickness of the inclusion and shaking intensity. The results of the analyses indicate that - as in the case of non-yielding walls - the isolation efficiency, in general, increases with increasing inclusion thickness and also depends on shaking intensity, wall height and excitation frequency. However, in contrast to the case of non-yielding walls, the isolation efficiency of yielding walls increases with inclusion thickness only up to a limiting value which cannot be exceeded with a further increase of inclusion thickness. For the case of EPS 100 (i.e., rho(EPS) = 20 kg/m(3)) a compressible inclusion with a relative thickness of 15% to 20%, can reduce the seismic pressure by up to 20%, and the seismic displacement increment of a wall by up to 50%, depending on shaking intensity and height of wall. Finally, it was shown that the excitation frequency as well as its relative value, with respect to the natural frequency of the wall-backfill system, is an important parameter which affects the seismic isolation efficiency of EPS and its dependence on shaking intensity, and particularly the isolation against wall rotation. It is concluded that EPS compressible inclusions can provide an effective means for reducing the permanent seismic displacement and lateral thrust increments for new or existing seismically retrofitted yielding earth retaining structures. (C) 2012 Elsevier Ltd. All rights reserved.
